The Effect of Flow-Related Aneurysms on Hemorrhagic Risk of Intracranial Arteriovenous Malformations

BACKGROUND: Previous reports indicated an association between hemorrhagic presentation and flow-related aneurysms in arteriovenous malformation (AVM) patients. However, it remains unclear whether these flow-related aneurysms result in the hemorrhage of AVM. OBJECTIVE: To characterize this hemorrhage risk using our institutional experience over 25 yr. METHODS: We retrospectively reviewed records of patients at our institution diagnosed with AVM from 1990 to 2015. Patients without associated aneurysms (AVM only) and those with flow-related aneurysms (AVM-FA) were compared. Those with intranidal or unrelated aneurysms were excluded. Annual risk of AVM-related hemorrhage was calculated using the birth-to-treatment approach and compared using Poisson rate ratio test. RESULTS: Among 526 patients, there were 457 AVM only patients and 69 with flow-related aneurysms. AVM-FA patients were older (P =. 005). AVMs with flow-related aneurysms were more likely located in the cerebellar vermis and hemispheres (P =. 023 and. 001, respectively). Presence of flow-related aneurysms increased the risk of presentation with subarachnoid hemorrhage (P <. 001). Interestingly, no significant differences in presenting hemorrhage due to AVM rupture were found (P >. 356). The majority of aneurysms were untreated (69.5%), and only 8 (9.8%) had ruptured presentation. At follow-up (mean = 5.3 yr), patients with flow-related aneurysms were less likely to develop seizures (P =. 004). The annual risk of AVM hemorrhage was 1.33% and 1.05% for AVM only patients and AVM-FA patients, respectively (P =. 248). CONCLUSION: Despite increased risk of subarachnoid hemorrhage at presentation, there was no increased likelihood of rupture in AVMs with flow-related aneurysms. More studies are warranted, as clarifying the competing risks of AVM vs aneurysm rupture may be critical in determining optimal treatment strategy.